Many studies have identified the first flush phenomenon and runoff characteristics. The purpose of this study is to elucidate which parameters influence the runoff pollutant loads. Eight runoff events during the period from May 1999 to September 2000 were investigated. From the dimensionless cumulative analysis, it was suggested that particulate substances such as suspended solids (SS), iron and total phosphorus (T-P) were inclined to be washed off in heavier rainfall condition. The cumulative curves of particulate constituents were appreciably variable in slope, while those of dissolved were approximately constant. Accordingly it was indicated that dissolved load was discharged regardless of rainfall conditions. Event mean runoff intensity and cumulative runoff height showed significant correlation with the cumulative runoff load of the constituents except for total nitrogen (T-N). On the other hand, antecedent dry weather period (ADWP) and traffic flow volume during ADWP did not show correlation with the cumulative runoff loads. Only T-N load showed correlation with those factors, consequently it was suggested that vehicular exhausts affected nitrogen load on the surface of urban highway.

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